Some aircraft rely on turboelectric distributed propulsion (TeDP) systems for powering propulsors that are placed around the airframe, for example, to provide thrust for controlling movement of the vehicle. Each propulsor may include a motor that drives a propeller fan and the electrical power used to drive each propulsor motor and fan may be generated by one or more on-board, turbo generators.
Slight variations in the speed of propulsor fans can have a dramatic impact on the amount of undesirable fan noise that is exerted from the aircraft. Some direct current (DC) type TeDP systems (through sacrificing size and weight) may reduce the perceptible peak sound pressure level by driving the propulsor fans at varying speeds using variable speed drives to spread the noise spectrum across more frequencies. Alternating current (AC) type TeDP systems require the speed of the propulsor motors to be synchronized with the speed of the other motors and the turbo generators. Accordingly, despite being smaller and lighter than DC-type TeDP systems, typical AC-type TeDP systems cannot vary the speed of the propulsor fans to spread the noise spectrum across multiple frequencies and therefore, may appear louder than some DC-type TeDP systems.